1. Field of the Invention
The present invention relates to a motion vector estimation, and more particularly, to a method for estimating a motion vector in a moving picture.
2. Background of the Related Art
An outline of an emerging Moving Picture Expert Group (MPEG) standardization, MPEG-4 will now be described. The MPEG-4 pursues a technique different from the techniques of MPEG-1 and MPEG-2 previously used to cope with the current trend in which boundaries of techniques of communication, computer and broadcasting are broken away into multimedia. That is, the object of MPEG-4 is a comprehensive technique that embraces each field of the above techniques and their independent technical innovations independently as well as the exploration of fields to which the new comprehensive technique is applicable. The directions that MPEG-4 pursues at large is a technique that allows an Audio and Video (AV) coding at an extra low bit rate.
To realize the technique that allows an AV coding at an extra low bit rate, the following techniques are suggested. First, a new coding technique in which the MPEG-1 and MPEG-2 DCT transform technique is not used, for example, the Wavelet coding system that has less distortion at block boundaries and a high coding efficiency. Second, a technique that conducts motion compensation in a manner other than the MPEG-1 and MPEG-2 block based motion compensation, which conducts the motion compensation by a macro block unit. Third, a region based coding technique inclusive of the contour coding technique and the object oriented coding technique. Fourth, a Fractal coding technique that can make a compression ratio over 1/1000.
Further, there are 8 new techniques that are not yet realized but are trying to be fully realized in MPEG-4. The eight new techniques include improvement of a coding efficiency, scaleability matching to a content, content handling and bit stream editing, improvement of tolerance for error, access to a multimedia data base, coding of a plurality of synchronous data, hybrid coding of natural data and synthesized data, and improvement of a random accessibility at an extra low bit rate.
A related art method for estimating a motion vector will be explained with reference to FIGS. 1a-1c that illustrate 8.times.8 block matrices having pixel weighted values according to a related art Overlapped Block Motion Compensation (OBMC).
Additional methods for estimating and compensating a motion vector suggested during the MPEG-4 standardization process include a method for estimating and compensating a motion vector suggested by Sharp, in which a multimode warping prediction is employed and a variable block size motion estimation suggested by Nokia. These methods have excellent characteristics, however, they are computationally complex.
In a current mode of motion vector (MV) estimation method in the MPEG standard, a two stage motion estimation technique is employed. In the two stage motion estimation technique, motion vectors are estimated by a 16.times.16 macroblock unit. However, for portions of the motion vector with relatively large errors, the motion vectors are estimated by a 8.times.8 block unit. Further, Overlapped Block Motion Picture (OBMC) is applied as a motion compensation technique to H.263. These motion estimation and compensation techniques are effective in the removal of blocking artifacts that occur in a motion estimation part.
The operational flow of a related art two stage motion estimation and compensation techniques now will be explained. First, in an advanced mode where 16.times.16 macroblock motion vectors are searched, 8.times.8 block motion vectors are searched with a search region of .+-.2.5 pixels in x and y directions with a center of the search on the already searched 16.times.16 macroblock motion vector. Then, the operational flow proceeds to OBMC, in which, if we assume that a pixel value for a reference frame is p(i,j) and a pixel value for a new frame is p(i,j), EQU p(i,j)=(q(i,j)*H.sub.0 (i,j)+r(i,j)*H.sub.1 (i,j)+s(i,j)*H.sub.2 (i,j)+4)//8
where, EQU q(i,j)=p(I+MV.sub.x.sup.0,j+MV.sub.y.sup.0), EQU r(i,j)=p(I+MV.sub.x.sup.1,j+MV.sub.y.sup.1), EQU s(i,j)=p(I+MV.sub.x.sup.2,j+MV.sub.y.sup.2).
FIGS. 1a-1c illustrate pixel weighted values in a related art OBMC process, which can inhibit occurrence of the blocking artifacts in the motion estimation part.
The related art method employs the two stage motion estimation technique in which the motion estimation is conducted by a 16.times.16 macroblock unit, and, then again, by an 8.times.8 block unit for portions that have a comparatively greater error. Thus, the related art method for estimating a motion vector in a moving picture, which uses the two stage motion estimation technique and the OBMC, has an increased computational complexity and a low efficiency. Accordingly, the related art method causes problems because the method can not deal with MPEG-4 whose object lies on facilitating an AV coding at an extra low bit rate.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.